PREDICTING THE BREAKING DORMANCY AND THE TRANSITION OF FLORAL BUD PROGRESSION FOR THREE PEACH CULTIVARS (Prunus persica (L.))

Abstract

Phenological changes have been observed in peaches during the last decades caused by the seasonal variability in climate conditions mainly experienced during dormancy, consequently affecting crop management practices, production, and harvest dates. This study focuses on field and lab evaluations of three peach cultivars (Prunus persica L.). Data was collected at the Chilton Experimental Research Center and processed in the lab under different controlled conditions. Two different seasons of data were collected (2021-2022 and 2022-2023). A model was developed to establish the amount of chilling and heat requirements needed to determine the beginning of the dormancy release in the cultivars. The model forecasts the period of dormancy, being relevant information for supporting practices including crop protection from possible cold damage. Economic and historical importance aspects of peaches, and a brief literature review of concepts, crop growth and development, weather implications in peach production as well as, the challenges of peach cultivation are presented in Chapter One. Some of these descriptions will be expanded in the next chapters. The model for the bud dormancy release in three peach cultivars is presented in Chapter Two. The budbreaks were modeled for selected commercial peach cultivars ‘Rubyprince, ‘Harvester’ and ‘Red Globe’. Using dormant shoots, the dormancy release through time was monitored under controlled conditions. A long-time record temperature database was used to calculate thermal requirements. Five different mathematical models were assessed including the Growing Degree Model, the Weinberger model, the Modified Weinberger model, the Utah model, and the Dynamic model. The chilling accumulation was different considering the season evaluated. Vegetative and floral buds reached the budbreak in the same months (January, February, and March) for seasons one and two. Results showed that cultivars evaluated needed a range from 137 to 207 days to get the budbreak in season 1 and 123 to 200 in season 2 starting from September as the initial date for the experiment. The Dynamic model allowed knowledge of the dormancy and budbreak process by combining both chilling and heat needs. Important base information for growers and industry has been generated. Weather data for 24 seasons (1998-2023) from the same experimental station located in Chilton, AL, were used to accumulate the chilling hours to demonstrate the variability of this requirement during that period.

Chapter Three refers to the post- dormancy process, where the bud progression for each cultivar based on Growing Degree Days were predicted. The prediction of progression was assessed using the same samples collected during the first period of the experiment. Through daily observations, we identified the transition among stages using the peach growth stages described in the Southeastern Peach Growers’ Handbook. A logistic model was performed to estimate the percentage values in the bud progression using a statistical measurement of Root Mean Square Error (RSME), and the line 1:1 for Observed vs Predicted values. After dormancy release, samples needed between 27 to 35 days to reach the full bloom stage and a range of 509.5 and 1054.5 GDD. The understanding of the different phenological states in species with economic importance such as peaches is related to important modifications in temperature patterns, being a good indicator of climate variations. The information provided by this study facilitates the understanding of plant responses and supports the production practices and agricultural adaptation, mainly, in the selection of resilient cultivars to local and climate conditions. This study closes with general conclusions and recommendations in Chapter Four.